diff --git a/docs/build.sh b/docs/build.sh
index 1b8cac8b06fa..b959b159c40b 100755
--- a/docs/build.sh
+++ b/docs/build.sh
@@ -44,11 +44,11 @@ rm -rf "${GENERATED_RST_DIR}"
 mkdir -p "${GENERATED_RST_DIR}"
 
 source_venv "$BUILD_DIR"
-pip install -r "${SCRIPT_DIR}"/requirements.txt
+pip3 install -r "${SCRIPT_DIR}"/requirements.txt
 
 bazel build ${BAZEL_BUILD_OPTIONS} @envoy_api//docs:protos --aspects \
-  tools/protodoc/protodoc.bzl%proto_doc_aspect --output_groups=rst --action_env=CPROFILE_ENABLED \
-  --action_env=ENVOY_BLOB_SHA --spawn_strategy=standalone --host_force_python=PY2
+  tools/protodoc/protodoc.bzl%proto_doc_aspect --output_groups=rst --action_env=CPROFILE_ENABLED=1 \
+  --action_env=ENVOY_BLOB_SHA --spawn_strategy=standalone --host_force_python=PY3
 
 # These are the protos we want to put in docs, this list will grow.
 # TODO(htuch): Factor this out of this script.
diff --git a/tools/protodoc/BUILD b/tools/protodoc/BUILD
index 8e428b5d24fd..b4b3c3f39acb 100644
--- a/tools/protodoc/BUILD
+++ b/tools/protodoc/BUILD
@@ -3,7 +3,7 @@ licenses(["notice"])  # Apache 2
 py_binary(
     name = "protodoc",
     srcs = ["protodoc.py"],
-    python_version = "PY2",
+    python_version = "PY3",
     visibility = ["//visibility:public"],
     deps = [
         "@com_envoyproxy_protoc_gen_validate//validate:validate_py",
diff --git a/tools/protodoc/protodoc.py b/tools/protodoc/protodoc.py
index bf6a869f0797..562d6de2ac5f 100755
--- a/tools/protodoc/protodoc.py
+++ b/tools/protodoc/protodoc.py
@@ -6,9 +6,9 @@
 from collections import defaultdict
 import cProfile
 import functools
+import io
 import os
 import pstats
-import StringIO
 import re
 import sys
 
@@ -709,7 +709,7 @@ def GenerateRst(proto_file):
 def Main():
   # http://www.expobrain.net/2015/09/13/create-a-plugin-for-google-protocol-buffer/
   request = plugin_pb2.CodeGeneratorRequest()
-  request.ParseFromString(sys.stdin.read())
+  request.ParseFromString(sys.stdin.buffer.read())
   response = plugin_pb2.CodeGeneratorResponse()
   cprofile_enabled = os.getenv('CPROFILE_ENABLED')
 
@@ -724,14 +724,14 @@ def Main():
     f.content = GenerateRst(proto_file)
     if cprofile_enabled:
       pr.disable()
-      stats_stream = StringIO.StringIO()
+      stats_stream = io.StringIO()
       ps = pstats.Stats(pr,
                         stream=stats_stream).sort_stats(os.getenv('CPROFILE_SORTBY', 'cumulative'))
       stats_file = response.file.add()
       stats_file.name = proto_file.name + '.rst.profile'
       ps.print_stats()
       stats_file.content = stats_stream.getvalue()
-  sys.stdout.write(response.SerializeToString())
+  sys.stdout.buffer.write(response.SerializeToString())
 
 
 if __name__ == '__main__':